Hermetic compressors are most commonly operated in a vertical orientation so that lubrication for the shaft, bearings, running gear, etc., is, typically, supplied by a passive centrifugal pump incorporated into the drive shaft. Oil is drawn from a sump which is located at the bottom of the compressor shell and enters the pump through an orifice in the bottom of the shaft. The parts requiring lubrication are, normally, no more than a foot or so above the oil level of the sump so that a small increase in the oil pressure due to its radial acceleration in sufficient to supply the oil to the required locations. This relatively simple, passive lubrication system is a primary reason why most hermetic compressors are designed to operate in a vertical position. In this orientation, the compressor height-to-diameter ratio is generally two, or more. By comparison, a typical reciprocating compressor of the same capacity has a height-to-diameter ratio of approximately 1.5.
For many applications, the height of the compressor is a primary factor because of packaging considerations. Very often, the height of an air conditioning, refrigeration or heat pump unit is more important than its width or depth. Accordingly, a distinct advantage could be realized if the compressor could be designed to operate in a horizontal orientation. However, in changing the orientation of a hermetic compressor from a vertical to a horizontal orientation, there are significant changes in the lubrication system and gas flow paths. The motor, cylinder, and running gear will extend below the level of the oil in the sump although it is not necessary that all of the members be exposed to the oil sump. The parts to be lubricated are located no more than a few inches above the sump as opposed to a foot, or more, in a vertical unit, but the drainage paths are shorter and over different parts. The oil sump blocks some normally used gas paths which are used in cooling the motor and removing entrained oil and some of the drainage paths can contribute to oil entrainment.